Cathode for electron discharge devices



1932. A. MAVROGENIS CATHOD'E FOR ELECTRON DISCHARGE DEVICES Filed Nov. 26, 1926 Patented Dec. 13, 1932 FFIQE ABISTOTE MAVROGENIS, OF MILWAUKEE, WISCONSIN CATE'IODE FOB, ELECTRQN DISCHARGE DEVICES Application filed Hovemeer 26, 2.928. .Eerial No. 156,,54A.

T his invention relates to cathodes for electron discharge devices.

T he present application is a continuation in part of my earlier application Serial No.

E 652,266, filed July 18, 1923, for Rectifier, part of which has matured into United States Patent No. 1,671,598 of May 29, 1928.

In electron discharge devices, such as vacuum tubes, it has been the practice hereto- 1,) fore to provide filamentary cathodes and under certain conditions, to coat these cathodes with thermioniCally active material. These cathodes have been of relatively short life and rapidly evaporate when in'operation'.

Another object of the invention is to provide, for an electron discharge devicedetector amplifier or the like-an equipotential or indirectly heated electron emitting cathode which is actuated by thermal means including a gaseous discharge device.

Another object is to provide an equipotential or indirectly heated cathode, for an electron discharge device, in which the cathode heating or activating means itself is adapted to be energized with alternating, fluctuating,

or direct current.

Another object of the invention is to provide, for an electron discharge device adapted to be used in a signal energy receiving sy tem or the like, an equipotential or indirectly heated cathode, which is so designed that the alternating or fluctuating current thermionically activating the cathode does not unduly interfere with the signal energy in the operation of the device.

A further object is to provide a cathode which has a conducting, thermionically active, firmly adherent coat on the outer surface of a silica or glass tube, or a tube of similar 40 insulating characteristics enclosing gaseous discharge thermal means.

They are of very small diameter and are fragile and hard to handle in assembling the parts of the tube, and frequently break in shipping, and as is well known, very often burn out.

It is to be noted further that the trend of the present practice is to apply a relatively -ti voltage to the filamentary cathode and a relatively high'voltage to the plate. A mistake connections or in changing the batteries, frequently results in instantly burning out these cathodes.

Further objects are to provide a novel formv of cathode, which is adapted for operation "from industrial lighting mains without requiring the use of accessories, and which may be so constructed that in the event that a higher voltage is applied to the plate of the tube than that of the mains, such cathode may also receive this higher voltage and operate efiiciently at such voltage.

Further objects are to provide a cathode which is heated by a gaseous discharge, and which is devoid of filaments or other heaters of this general type, and which, therefore, is not subject to burning out or rapid deterioration.

Embodiments of the invention are shown in Y the accompanying drawing in which:

Figure 1 1s a view of one form of cathode, such View being partly broken away and partly in section Figure 2 is an enlarged sectional view of the lower portion of one oil the arms of the cathode;

Figure 8 is a view of a modified form;

Fi ure d is a view of a further modified D 1 form of cathode;

Figure 5 is a fragments-.1 view of a cathode similar to that disclosed in Figures 1 and 4 and showing asl T1 n nigure 0 1S cathode.

r 11 leis e ht modification thereot';

a view of a further form of ration with one e h pin siren a c c l 4] J1 e or tie iOllRb also adapted to operate in a vacuum tube of the general type disclosed in my prior Patent No. 1,57O, l4l i, of January 19, 1926, for wireless apparatus, hlo. 1,638,499, of August 9, 1927, for electron dis charge device, No. 1,616,914, of February 8, 1927, for electron discharge device, No. 1,629,171, of May 17, 1927, for electron discharge device, and as disclosed in in copending application, filed November 3, 1926, Serial No. 145,940.

Referring to Figures 1 and 2, it will be seen that the cathode comprises a silica or glass tube 1 which is provided with two branches forming roughly a V and provided at their lower ends with enlargements or bulbs 2, and at their upper or joined ends with a relatively larger bulb 3. The bulb 3 may initially have an evacuating tube which is firmly sealed and forms a tip, such as indicated at 4. Preferably, the bulbs 2 and 3 are opaque and the tubes 1 are transoarent. In the form shown in Figures 1 and 2, the tube has a thickened or enlarged, opaque, shoulder portion intermediate its ends. The tube is provided with a plurality of equipotential or indirectly heated cathode POIF tions, such as indicated generally at A, B, and (1.. Preferably, the portion C is a double area of either the portions A or B. Each of portions is formed by means of a metallic sheath or coating 6 which is formed on the tube in a manner hereinafter described, and which is itself coated or formed with a low allinity oxide coating, as indicated at 7 in a manner hereinafter described.

Conductors 8, 9, and 10 lead to the portions A, B, and C.

Electrodes are sealed in the several bulbs, as indicated, and comprise electrodes 11 and 12 in the bulbs 2 and an electrode 13 in the bulb 3, the surface of the electrodes 11 and 12 may be substantially equal, and that of the electrode 13 may be substantially the sum of the surfaces of the other two electrodes. These electrodes are preferably formed of aluminum, tungsten, molybdenum, platinum or alloys thereof with magnesium, and preferably coated with any low aflinity oxide or any alkali metal which aids in starting ionization.

The tube is exhausted to a very high degree, and is filled with a suitable gas, such as helium, argon, neon, hydrogen, Xenon, krypton, or a mixture of any two or more of such gases. It has been found that helium, and

neon, with aluminum electrodes, require a very low initial potential to start ionization.

As a specific instance, it may be mentioned that the pressure of the gas in these tubes may be from two to ten millimeters of mercury,

that the distance between electrodes may be from two to three centimeters, and that the diameter of the tube may be one or more millimeters. This type of a tube will de velop a few watts sufficient for operation of the equipotential or heated cathodes.

It is to be particularly noted that the characteristic of these tubes is such that for a given pressure a certain predetermined voltage is required, and that any increase in voltage does not result in an increase in generation of heat, but instead causes a diminution of heat. Obviously, the requisite voltage is controlled in the design of these tubes by numerous fac indirectly tors within the control of the maker, such as the spacing of electrodes, their size, the diameter of the tubes, the pressure of the gases, the character of the gases, and the material of the electrodes. Therefore, the maker has at his command numerous facts by means of which he can produce gaseous discharge heaters for the equipotcntial r indirectly heated cathodes having the exact characteristics desired.

it is to be noted further that these tubes are adapted to start at the predetermined voltage so that no accessories for starting them are required. Instead, as is well known, there are always present some free ions which when tae electrodes are energized are attracted to their respective electrodes and acqu' 'e enormous velocities. The collision of ti ions with molecules of the gas produce other ions which, in turn, by collision produce still others. In this manner, the gaseous discharge will initiate itself upon the application of the requisite voltage, and the need of auxiliary apparatus is wholly avoided.

It is to be noted further that the heating of these tubes is uniform from one end to the other, and that substantially and for all practical purposes, all of the energy liberated is transformed into heat. The transparent tubes of these cathodes are surrounded by opaque tl'iermionically active coatings, so that light is not radiated but is converted into heat and is added to the heat directly generated by the tube. urther than this, the opaque end bulbs prevent the radiation of energy in the form of light or heat and, consequently, the maximum c'lficiency for these gaseous types of electrodes is secured.

It is to be noted particularly that the Voltage required for operation of these tubes may be anything that is desired. For example, the tubes may be operated directly from 110-volt al ernating or direct current mains or, if desired, they may be made so as to use efficiently, current supplied at a voltage equal to that furnished the plate of the tube with which these cathodes cooperate. Thus, it is possible to make vacuum tubes of various designs having characteristics, as noted in my above mentioned patents and copending application which require only four prongs.

It will be seen that these be burned out or destroyed application cathodes can not by the accidental thereto of a higher voltage than that for which they are designed. In the case of the ordinary vacuum tube having a filamentary heater or cathode, burning out is a frequent source of danger, as the instantaneous application of excessive voltage to the filament causes the burning out of the filament. This, as is well known, frequently happens with ordinary types of tubes. This defect, however, is not present with the oathode forming the subject matter of this invention, as the application of excessive voltage to the gaseous discharge tubes does not injure them and does not cause the generization of excessive heat. Instead, the actual amount of heat generated falls 0E instead of increasing, as previously pointed out.

The construction illustrated in Figures 1 and 4 is such that the tubes may have considerable length without having an excessively great spacing between the electrodes. For example, the electrodes 11 and 12 are connected to one supply terminal, and the electrode 13 to the other terminal. Thus, the length of travel from an electrode of one polarity to an electrode of the opposite polarity is no greater than the distance between either the electrodes 11 or 12, and the electrode 13.

In the form of the invention shown in Figure 3, the same inventive idea is employed except that a straight or single cathode is provided. This consists of a tube 14 similar to those previously described having bulbs 15 at its ends- These bulbs carry electrodes 16 and 17. The tube is surrounded by a metallic sheath 18 which has a connecting extension 19 projecting therefrom. This metallic sheath may be formed either by coating or else may be made of a metal tube and slipped on the glass tube 14 prior to the sealing thereon of one of the end bulbs. At all events, the outer surface of the metallic sheath 18 is coated or formed with low affinity oxides.

Figure 4 shows a form of the invention substantially identical to that previously described in connection with Figure 1, the only difference being the omission of the enlargements 5 of the glass tube. Instead of this, spaces 20 are formed between the conducting cathode coatings.

In the form of the invention shown in Figure 5, the same construction is followed with, however, the exception that the bulbs, such as indicated at 21, may be transparent and may have an opaque coating 22, preferably, of metallic material and acting as a reflectorto reflect heat and light waves back into the device, and thus prevent loss, or otherwise coated or frosted inside or outside.

In the form of the invention shown in Figure 6, the upper electrode is omitted and only two terminals, as indicated at 23, are employed. These terminals lead to electrodes corresponding to the electrodes 11 and 12 described in connection with Figure 1. The discharge is from one electrode completely around the V-shaped tube to the other electrode. This type of cathode, therefore, provides for the use of higher voltages than those disclosed in the other figures. Otherwise, the operation of the device is the same as that previously described. In this connection, it may be added that preferably three cathode surfaces are formed, as indicated at A, B, and C, and that the connecting terminals 24, 25, and 26 extend from these surfaces.

Several different processes may be followed for forming the metallic coatings and the oxide coatings on the cathode. For example, one process consists of coating the dielectric or glass tube with first a metallic coating formed from chlorides of platinum, palladium, rhodium, ruthenium, iradium, osmium, nickel, or silver, or compounds or mixtures of any two or more of these metals,

as disclosed, for example, in my co-pending application, Serial No. 140,848, filed Oct. 11, 1926, for cathode and method of making same. Afterwards the metallic coating is itself coated with low electron afiinity oxides, barium, strontium, or calcium, or the like, or mixtures of such oxides. Further, the glass tube may be coated with a mixture of about six percent of the low electron affinity oxides mentioned above, and of any metallic electrically conducting chlorides, for example, ninety-four percent of any of the chlorides or mixtures thereof, as described above.

A further process that can be followed with these cathodes is to employ nickel, silver, gold, platinum, palladium, or others of the metals mentioned above containing compounds electrically conducting, and form a paste of these compounds using water, alcohol, or any liquid in which such compounds are soluble, or else the metals mentioned above may be employed in the colloidal form and applied as a colloidal solution to the glass. It is intended that in these cases the liquid is either wholly absorbed or evaporated prior to using the cathode.

A further method is to employ any of the metals ust mentioned in the form of a liquid bath in which the cathode is dipped. Further, the low ailinity oxide coating may be formed upon the metal coating by dipping such partially coated cathode into a melting bath of alkaline metals or their oxides, or other compounds, particularly the metals, such as barium, strontium, and calcium. Further, the melted solution or even the mixture may have both the noble metal, as well as the low electron ailinity oxides therein.

A further method may be followed which consists in dipping the cathode into a melted solution containin approximately ten percent of alkaline metals and ninety percent of the main metals mentioned above. There after, the cathode, after cooling is baked preferably in a vacuum to the melting point of the oxides, whereby a film of oxides covers the whole of the cathode structure and both the metallic and thermionically active coatings are formed.

A further method may be followed which consists in using a solution of any of the noble metals containing metallic compounds and any of the alkaline earth groups of metals, as well as a chloride, preferably of nickel, platinum, or palladium, or similar material. Further, calcium chloride can be employed in this mixture. This mixture is made with water or other suitable liquid, and is applied to the cathode, such cathode being dried and baked in air, or in vacuum. Obviously, the baking may be in a furnace or may be produced by passing current through the cathode itself, or else both of these expedients may be simultaneously used.

It is to be noted that in all of these processes, means are provided for forming a semi-adherent conducting coating upon the glass or other dielectric, and providing this coating with low afiinity oxides.

It is to be noted further that the processes mentioned above may be expeditiously followed and that a substantialy rugged and reliable cathode will result.

It is to be understood that the terminal of the electrodes of the gaseous discharge device may be made relatively rigid so that they can be used as supports for the cathode.

It is to be noted that in practicing this invention a solid unitary equipotential cathode is provided.

This cathode may be used in any capacity for electric disc-barge device, and may replace the ordinary filamentary cathodes. F urthcr, it is apparent that the cathode due to its unitary nature may be easily handled, mounted, and assembled in the device in which it is employed.

Further than this, as pointed out in detail above, it is apparent that the cathode is automatically self-regulating so that no damage can occur, although excessive voltage may be inadvertently applied to the terminals of the gaseous heater. Further, it is to be noted that no damage can occur to the audion plate with which this device is used, even if excessive voltage is applied both to the audion plate and to the heater, due to the fact that the automatic characteristics of the heater, in reality, cuts down the electron emission of the cathode and, consequently, prevents damage to the andion plate even when excessive voltage is applied.

It will be seen, therefore, that this novel form of cathode acts in a manner impossible with the ordinary types of cathodes, and that it is self-protecting and protects the other portions of the electric discharge device with which it may be used.

The electrodes for the gaseous dischargr device may take any desired form provided its correct surface is secured. For instance, they may be disc like, as shown, spherical, or of other shapes.

It is to be understood that while the electron emitting surface is directly insulated from the heating means within the cathode, that nevertheless such electron emitting surface may be connected by leads or conductors with either terminal of the cathode gaseous discharge heating means, and that this connec-tion may be made either outside or inside the envelope of the device with which the cathode is used, depending upon the particular demands or design of the device in which the cathode is used.

Although the invention has been described in considerable detail, such description is intended as illustrative rather than limiting as the invention may be variously embodied and the scope of such invention is to be determined as claimed.

I claim:

1. An indirectly heated cathode for electron discharge devices comprising a gaseous discharge heat radiating body and an electrically conducting element serving as an electron emitter and closely surrounding said hea radiating body, all of said parts being formed as a unit, said electrically conducting element being directly electrically insulated from said heat radiating body.

2. An equipetential, thermally activated cathode for electron discharge devices comprising a gaseous discharge heating element, and an electrically conducting body coated with a low electron affinity substance arranged in close proximity to said heating element and serving as an electron emitter, all of said parts being formed as a unit, said electrically conducting body being directly electrically insulated from said heating element.

3. A cathode for electron discharge deyices comprising a gaseous discharge heatmg element, and an electrically conducting, electron emitting body closely surrounding said heating element and thermally activated by said heating element, said electrically con ducting body being formed of high refractory material and of a low electron affinity substance, all of said parts being formed as a unit, said electrically conducting body being directly electrically insulated from said heating element.

4-. An indirectly heated cathode for electron discharge dcvices comprising a thermionically active electron emitting heated surface, a gaseous discharge heat radiating body positioned within said surface for thermally activating said surface, and electric lead-in conductors connected to the terminals of said heat radiating body, said heated surface being directly electrically insulated from said heat radiating body.

5. An equipotcntial cathode for electron discharge devices comprising a gaseous discharge heating element and a thermionically active coating serving as an electron emitter formed on the outside of said heating element and thermallyactivated by said heating element, said coating being mechanically distinct and directly electrically insulated from said heating element.

6. An indirectly heated cathode for electron discharge devices formed as a unitary member and comprising a gaseous discharge heating element, an electrically conducting coating formed on said heating element and being thermally activated thereby, and an outer coating of a low electron aiiinity substance formed on said conducting coating, said conducting coating being directly electrically insulated from said heating element when in operation.

7. An indirectly heated cathode for electron discharge devices comprising an electrically conducting and thermionically ac-' tive member serving as an electron emitter, and a gaseous discharge heating element positioned within said member for thermally activating said member, said heating element including an electrically insulating vessel, a gas within said vessel, lead-in conductors sealed in said vessel, spaced electrodes within said vessel connected to said conductors, said device being adapted to start and maintain a gaseous discharge within said vessel, said active member being directly electrically insulated from the gaseous discharge of said heating element.

8. An indirectly heated cathode for electron discharge devices comprising a thermionically active and electrically conducting coating serving as an electron emitter, a gaseous discharge heating element positioned within said coating for thermally activating said coating, electric lead in conductors embedded in said coating, and lead-in conductors connected to the terminals of said heating element and being relatively rigid and acting as supports for said cathode. said coating being directly electrically insulated from said heating element when in operation.

9. An equipotential cathode for electron discharge devices comprising an electrically conducting and thermionically active body serving as an electron emitter and being thermally activated, and a gaseous discharge heating element positioned within said body, said heating element including a vessel provided with a plurality of enlargements. an electrode mounted within each of said enlargements, lead-in conductors connected to said electrodes and passing outwardly from said enlargements. and a gas within vessel. said active body being directly electrically insulated from the interiorot said vessel.

10. An equipotential cathode for electron discharge devices comprising a silica tube, a thermionically active and electrically conhaving opaque enlargements at its ends, electrodes mounted withinsaid enlargements, lead-in conductors connected to said electrodes and passing outwardlythrough said enlargements, a gas carriedwithin said tube. 5

and said enlargements, anda plurality of distinct and separate conducting and electronically active coatings serving as thermally activated. electron emitters and being formed on the outer side of said tube, said coatings being directly electrically insulated from the 7 interior of said tube.

12. An indirectly heated cathode for electron discharge devices comprising a pair of tubes oined at one end by a bulb and havingbulbs at their other ends, electrodes located in said last mentioned bulbs, an electrode having a greater surface than said first men tioned electrodes and located in the first mentioned bulb, said tubes and bulbs being filled-- with a rarefied gas, and electrically conduct- Y ing thermionically active, electrically dis- .tinct coating formed on said .tubes, and adapted to serve. as electron emitters.

13. An indirectly heated cathode compris- 1 ing a sealed, refractory, electrically insulating tube having subatmospheric pressure therein, electrodes located within said tube,

means for conducting current .to said electrodes for heating said. tube by an electrical gaseous discharge within saidtube, and an indirectly heated cathode located on the outer side of said tube and being thermally activated and directly electrically insulated from everything within said tube during the operati on of said device.

14.,A multiple indirectly heated cathode for electron discharge devices comprising gaseous discharge heating means. and a plurality of electrically distinct conducting and thermionically active bodies serving as electron emitters closely surrounding said heating means and being thermally activated by said heating means, said conducting bodies being distinct and separate fromeach other-- and being directly electrically insulated from i said heating means.

15. A multiple equipotential cathode for electron discharge devices comprising a plurality of electrically distinct conducting mem-- bers having thermionically active surfaces 1 serving as electron emitters, and a gaseous discharge heating element positioned Within said conducting members activated thermally by said heating element, and means connected to said heating element and being operatively independent of said conducting members for supplying current to said heating element, said conducting members being distinct and separate from each other and being directly electrically insulated from said heating; element when in operation.

16. A multiple indirectly heated cathode for electron discharge devices formed as a unitary member and comprising a plurality of electrically distinct conducting and thermionically active members serving as electron emitters and being thermally activated, and a gaseous heating element associated with each of said members said heating element including an elongated vessel having electrodes therein and conductors sealed in said vessel and connected to said electrodes, said active members being directly electrically insulated from the interior of said vessel.

17. A multiple equipotential cathode for electron discharge devices comprising gaseous discharge heating means, and a plurality of electrically distinct conducting and thermionically active coatin s serving as electron emitters on said heating means and being thermally activated by said heating means. said conducting coatings being distinct and separate from each other and being directly electrically insulated from said heating means, and being distinct from said heating means.

18. A multiple equipotential cathode for electron discharge devices formed as a unitary member and comprising a gaseous discharge heating: element, a plurality of electrically distinct conducting metallic coatings formed on said heating element and being thermally activated by said heating element. each of said outer coatings and each of said metallic coatings being distinct and directly electrically insulated from said heating element.

In testimony that I claim the foregoing I have hereunto set my hand at Milwaukeefln the county of Milwaukee and State of Wisconsin.

ARISTOTE MAVROGENIS. 

